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Revision as of 06:57, 3 November 2009

At first glance, all A-series cylinder heads look alike. But by careful notice of specific features you can identify the model.

1 Early or Late?
2 A12GX Head Identification
3 Port Shape
- 3.1 Exhaust Ports
- 3.2 Intake Ports
4 Head Front Face
5 Spark-side Bosses
6 Manifold-side Bosses
7 Alternator Mounting
8 A12GX Identification

Early or Late?

To determine if the head is for an early (pre-1974) or late (1974-up) engine, check for existence of an oil passage here:

Only early engine have the passage in the head here. Of course, one can have the passage drilled on a newer head, but it is a good sign.

To double-check it is an original early head, look at the outside:

Early head: oil passage boss

Late head: no oil passage boss

A12GX Head Identification

One way to identify a GX, when the head is still installed: Look for the oil passage boss (indicating an early head), and for seven studs on the top of the inlet/exhaust manifold gasket. This combination is a good indicator of an GX (or A12T) head. Regular early heads have only five studs along the top of the gasket.

Port Shape

Early head with oval ports is either an A12GX head, or its twin, the early A12T head from the Nissan Cherry (E10). These are the high-revving heads for the factory Hitachi Twin Carb engines.

Exhaust Ports

All heads have nearly square exhaust ports.

Sizes:

Intake Ports

Round port 28mm: A12
Round port 28mm lowered: A14 GFU
Small Oval port 28x30mm: A13, A12A
Medium Oval port 28x34mm: A14
Large Oval port 30x34.5mm: A12GX engine

Head Front Face

3-bolt
4-bolt, adds high alt mount
4-bolt, adds high alt mount, with air passage
5-bolt, adds low alt mount
A14T H72 head

Spark-side Bosses

Look at the accessory/bracket mounting holes.

No bosses

One boss (undrilled, 1973?):

One boss (drilled, 1973?):

Three boss (late 1970s):

Manifold-side Bosses

Without boss, early B110
With boss, not drilled, later B110
With boss, drilled

X++

Without boss
- 5-bolt face:
With boss, not drilled, front boss drilled
With boss, drilled, front boss undrilled
With boss, drilled, no front boss

Alternator Mounting

Left Side

B10,B110: on left side of engine, down low
- Upper bracket bolts to front face of head

Right Side

B210: up high.
- Upper bracket bolts to Upper bolt hole on head
B310: up low.
- Upper bracket bolts to lower bolt hole on head

A12GX Identification

A true A12GX cylinder head has all these features:

Dual valve springs
No casting numbers
Large Oval port 30x34.5mm
- Ports are raised, and extend above upper intake bolts
27x29 mm exhaust ports
closed combustion chamber - heart shaped
- Large size combustion chamber of 29.1 cm3
large water holes (one under each intake port). Each hole is about the diameter of a pencil (newer heads have small holes)
Seven upper intake face bolts, nine bolt holes (vs only 5 for other pre-74 heads)
As with all pre-74 heads, Oil passage on head face (spark plug side)
- Boss on side, between plugs 2 & 3
SAME valve sizes as standard A12: 29mm exhaust, 35mm intake
NO bosses on side between plugs 1&2 and 3&4 (that indicates a newer head)

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Cylinder Head Identification